To observe diffraction, the size of an obstacle

The correct answer is Option (1) → Should be of the same order as wavelength

Diffraction occurs when a wave bends around the edges of an obstacle or passes through a narrow aperture. The effect is significant only if the size of the obstacle (or slit) is comparable to the wavelength of the wave. If the obstacle is much larger than the wavelength, the bending is negligible and straight-line propagation dominates. If it is much smaller, the wave passes without noticeable bending.

Answer: Should be of the same order as wavelength